Amplifier (audio system): Crackle & Hum on Touch Volume Control

I have an aging (perhaps even elderly) NAD 310 Stereo Integrated Amplifier, which nowadays is used nearly exclusively to connect my MacBook Pro to a pair of boomy Yamaha speakers. (I used to have other audio equipment plugged into some of the other audio in ports but I gradually stopped using the other devices; when I want to listen to music it’s either local MP3 files or it’s YouTube videos and hence sound from the computer either way).

There’s a worsening problem with the amp. When I plug in the laptop after being out and about and turn the amp’s power on, I won’t always get sound on one of the channels; moving the amp’s main volume control, or even just touching the volume knob, makes a loud crackle from the speaker and with luck (70% of the time) the sound on that channel kicks in; or instead I’ll get a loud hum and have to futz with it more.

Time to replace the amp, right?

There’s no likely scenario in which problems elsewhere (speakers, wires, computer, plugs) would cause this behavior with such sensitive and futzy response to the volume control, right?

Even just touching it? I’d wager it’s either static from your body or some type of capacitive mumble mumble EE word interference from you (inductance? coupling?).

In either case, what happens if you touch a metal part of the amp frame with one hand and then put your hand on the volume control? Touching the frame should bring you and the receiver to the same potential and it may reduce some of the crackle.

It could also be something as simple as a flaky volume control.

And, rereading something, I have to wonder if that channel is bad. I’d start by swapping the two speakers (swap the wires on the amp) and see if the problem stays with the speaker or the channel. If you can individually control the volume on the left and right speaker, play with that and see if it makes a difference.

I’d also suggest, before you pour out any money into this you make sure it’s actually the amp. I know it sounds like it is, but I’d either plug a different source into it or plug your laptop into something else.

Is your laptop on your lap when you’re doing this? If it is, put it on a desk so you can be sure there isn’t a little bit of current traveling through you, one way or the other, and causing something similar to a 60hz buzz/ground loop. You might also try unplugging your laptop to see if that changes anything.

How handy are you?

I personally would take some contact cleaner to the volume control before declaring it dead, but this does involve opening the case of the amplifier.

With the amplifier off and unplugged, open up the case, find the volume control potentiometer, look for a small hole on the side of the potentiometer, and spray in a bunch of contact cleaner. A can of contact cleaner usually comes with a small straw so that you can spray the cleaner directly into the potentiometer without spraying it all over everything else nearby. Once you have sprayed the cleaner into the potentiometer, turn the volume control back and forth all the way a whole bunch of times. This will remove a lot of the corrosion and built-up gunk inside the volume control.

A $7 can of contact cleaner is a lot cheaper than a whole new amp.

If you can conclusively associate it with the volume knob, it’s probably the volume knob. There aren’t a lot of moving parts on an amplifier but the knob(s) has a bunch of contact surfaces that a wiper sweeps back and forth upon and the point of contact can get dirty or corroded over time & use. It could also be the left/right pan knob if the amp has one.

Often, a generous squirt of contact cleaner inside the potentiometer can buy some time. You’ll probably have to open the amp to get to expose the pot in order to direct the cleaner to the proper spot. Let everything dry completely before powering back on.

The volume control knob is one of those dual knobs, with the left speaker knob being the “lower” one (lower on the spindle; closer to the amp) and the right speaker knob “above” it (closer to the person), so that each speaker’s volume can be raised or lowered independently, as opposed to one volume knob and a separate balance knob.

It’s the inner knob (left speaker volume knob) that is the hypersensitive one; it is difficult to rotate the right knob without the left speaker doing the crackle-hum-cutout-comeback routine, but if I carefully HOLD the inner left speaker knob stationary with a pair of fingers and twist only the outer right speaker knob, there’s (mostly) no misbehavior; moving the left speaker knob exclusively, it’s definitely that one that’s doing it.

The laptop is sitting on a stand, not on my lap.

I’ll see if I can disassemble it easily and, if I can, I’ll see if I can snag some of that contact cleaner stuff, thanks!

Before taking it apart, you may want to (while it’s off) rapidly move the volume knob(s) back and forth a few times. You don’t want to break anything, but if that makes even a small amount of difference, I’d be more inclined to believe that they/it just needs to be cleaned.

Also, be careful. If there’s any capacitors in there, especially large one, they can give you a good jolt even if the unit’s been unplugged for a while.
Typically you discharge caps by shorting them, I’m not sure if that’s allowed when you’re working with audio equipment and even if it is, you’ll likely not be able to access all the terminals of all the caps.

I’ll third, fourth, and fifth the contact cleaner approach. WD-40 makes a cleaner that is about $7 on Amazon…you’ll never use up the whole can. It’s non-conductive, leaves no residue, and hardly has any odor.

Coincidentally, I just used mine this morning on an older M&K MX-70B subwoofer that had developed a lot of static in the level control pot. I pulled the plate amp, sprayed into the sides of the pot three or four times (make sure to spray with the knob in various positions to ensure getting the cleaner on the wiper), worked the knob for a few minutes and PRESTO…problem was completely gone. You may have to repeat this every year or two, but it beats the heck out of buying a new unit or having it repaired.

Note on contact cleaners: DeOxit is one of the most popular brands out there. Spring for the “Gold” version. Used in reasonable amounts a can will last quite a while.

Note the reviews of it on Amazon.

I used DeOxit for years and it’s a great product, but I specifically suggested the WD-40 version because it works every bit as well for me and it costs less than half of what DeOxit costs.

Of course, the usual precautions should be observed.

I looked at the image search results for OP’s amp and there are a LOT of photos of this thing opened up. It looks pretty serviceable with plenty of space. There are two sides, one for the power supply and the other for ‘the rest’ of tbe amplifier. It seems some versions had a single toroidal transformer while others had a pair of more traditionally cored transformers. The power supply caps should be avoided but the ones on the amplifjer side should be safe enough. In any case, the volume gain potentiometer is easily accessed once the housing is opened up.

The NAD 310 seems well thought of, although considered a basic amp. (The actual design is - to say the least - unconventional). But as noted above should be a very easily serviced amp to just clean. The power supply related parts are well away from where you would be working. Just don’t work on it if it is plugged in.

I would note that at least three things can go wrong with the volume pot.
[ol]
[li]It could be contaminated, so a clean fixes things.[/li][li]It could be damaged so that a wiper is not making good contact with the resistive track.[/li][li]The resistive track could be worn away.[/li][/ol]

I have seen all three in older gear.

A clean with a proper electronic contact cleaner is the best start. Damage and wear need a new potentiometer. Easy if you know how, and have the tools. So, even if you do decide to replace the amp, don’t throw it out. I guarantee that there is a market for it, where a poor but knowledgeable geek will be all too happy to buy it cheap to fix it up, and it will have another 20 years of useful life. At this stage in its life replacing all the electrolytic signal capacitors would not be a bad thing, as by now some will be reaching the end of their life. Again, something for a poor geek.